1. Field of the Invention
This invention relates to a developing device suited for polychromatic reproduction, and more particularly to a developing device which enables the surface of a photosensitive medium to be developed always under the same conditions as it passes by a developing station.
2. Description of the Prior Art
In a typical design heretofore devised for developing electrostatic images of various colors formed on a photosensitive medium by a color copying apparatus, units for applying various color developers to the photosensitive medium are prepared corresponding to the number of the colors and juxtaposed closely adjacent to each other and along the path of movement of the photosensitive medium. One of these developing units which corresponds to the electrostatic image of a predetermined color is driven when such electrostatic image passes by the developing station.
In such a design, the mixture of distinct developers has been liable to occur between the juxtaposed developing units, thus resulting in a color mixture of reproduced image. Firstly, in such arrangement, it is necessary that one developing unit be operated while all the other developing units remain completely inoperative. Moreover, for example, in case of magnetic brush development wherein a magnetic brush is rotated to apply toner for development, the probability of toner scattering is so high that scattered toner is very likely to enter the adjacent inoperative developing units. This must be obviated by providing a suction duct for each of the developing units.
Thus, in the developing device of the described type, a very complex mechanism is required for the prevention of color mixture and the group of developing units occupies such a great space around the photosensitive medium as to limit the space for other process means.
Further, the juxtaposed relationship of the developing units gives rise to a difference in distance with respect to the location of the latent image forming means, especially, the exposure station, which would affect the conditions of development and accordingly the reproduced image.
Also, if the above-described developing device is applied with a drum-shaped photosensitive medium, the configurations of the developing units must be varied depending on the location of the developing device, and this leads to a disadvantage that the same standard or specification could not commonly be applied in the manufacture of the developing units.
In view of these points, the present invention provides a developing device which will achieve the following objects.